Shell Quantum Dots Research Articles

Temperature, hydrostatic pression and composition x effects on intersubband energy levels in ZnSe/ZnSxSe1-x core–shell quantum dot

In this paper, we have studied theoretically the effects of the, temperature, hydrostatic pressure and the composition on the intersubband transition energies. We have used a mathematical method, which based on a combination of coordinate transformation and the finite difference method. We have controlled the size and shape of core shell quantum dot CSQD by varying the parameters introduced in the function of coordinate transformation. We have studied the influence of hydrostatic pressure and temperature on the optical properties.

Novel synthesis of Mn: ZnSe@ZnS core–shell quantum dots based on photoinduced fluorescence enhancement

A novel Type-I Mn: ZnSe@ZnS core–shell quantum dots (QDs) was reported through a two-step procedure by using low-cost inorganic salts and naturalbiomacromolecule as raw materials. Based on a designed structure of L-cysteine-capped Mn: ZnSe QDs in aqueous media with the controllable surface, Mn: ZnSe@ZnS core–shell QDs were formed due to photoactive ions and defect curing under continuous constant light. The influences of experimental variables, including synthesis conditions of Mn: ZnSe QDs, different types and affecting factors of photo irradiation had been systematically investigated. Under the effect of photoinduced fluorescence enhancement, the photoluminescence (PL) intensity increases significantly by about 5–10 times after 1–3 h of UV irradiation. The position of the fluorescence peak was red-shifted by about 17 nm, emitting orange-red fluorescence. The photoluminescence quantum yield (PL QY) was markedly improved (up to 35%). The structure and morphology of Mn: ZnSe@ZnS core–shell QDs were also confirmed by Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDS) in detail. The mechanism of photoinduced fluorescence enhancement was attributed to L-cysteine allowed to release S2- to form a ZnS shell, and the passivated surface non-radiative relaxation centers of Mn: ZnSe@ZnS QDs was successfully synthesized with highuniform size, excellent photoluminescence performance, and good stability, all ofwhichmakethemgood potential candidates for white LEDs, and biological labels.

Smart quantum dot LEDs with simulated solar spectrum for intelligent lighting

LED light bulbs that simulate solar spectrum were fabricated using CdSe core–shell quantum dots in combination with GaN blue-light chips. They exhibited excellent optical properties such as white CIE coordinates of (0.33, 0.33), high color rendering index (CRI) of 98 and correlated color temperature (CCT) of 5352 K. Moreover, a circuit system was used to control the LEDs so that the lighting spectrum changes with the time in a day to simulate the actual solar spectrum. The results show that the sun-like spectrum smart bulbs not only have good optical properties and high electrical stability, but also can automatically adjust their spectrum according to the time, making the lighting natural. This work makes sun-like lighting conditions for some special environments to promote the application of smart bulbs in smart lighting.

Properties of Films Based on Nanosize and Submicrometer InSb Particles Passivated with CdS

An increase in the reflection in the IR spectral range typical of a plasmon resonance in single crystals is observed in an InSb film formed by thermal evaporation in a vacuum on a CdS single crystal. Raman spectra demonstrate an approximately constant ratio between the amorphous and crystalline phases for InSb films on a CdS substrate, which is uncharacteristic of an InSb film on gallium–gadolinium garnet. The current–voltage characteristics of an InSb film on CdS are linear, as also those of an annealed sheet of InSb (core)–CdS (shell) quantum dots and, in addition, become sensitive to illumination.

Effect of Confinement Strength on the Conversion Efficiency of Strained Core–Shell Quantum Dot Solar Cell

Effect of Confinement Strength on the Conversion Efficiency of Strained Core–Shell Quantum Dot Solar Cell

Reversible plasmonic switching in a graphene nanoresonator loaded with a core – shell quantum dot

A model of an all-plasmonic switch based on a graphene waveguide integrated with a stub nanoresonator loaded with a quantum dot is considered. Using the full-wave numerical simulation, it is shown that successive on/off switching of the control surface plasmon – polariton wave at the input of the waveguide leads to a change in the phase of the signal plasmon – polariton wave in the nanoresonator by π. This causes reversible switching of the device operation regime – from almost complete blocking to stable transmission of the signal plasmon – polariton wave through the waveguide. The effect is implemented at rates of ∼0.5 THz for infrared electromagnetic waves localised in a device with a switching region of 40 × 20 nm.

Quantum Confinement Effect and Photoenhancement of Photoluminescence of PbS and PbS/MnS Quantum Dots

The quantum confinement effect and photoenhancement of photoluminescence (PL) of lead sulphide (PbS) quantum dots (QDs) and lead sulphide/manganese sulphide (PbS/MnS) core shell QDs capped with thiol ligands in aqueous solution were investigated. From PL results, the presence of MnS shells gives a strong confinement effect which translates to higher emission energy in PbS/MnS core shell QDs. Increasing MnS shell thickness from 0.3 to 1.5 monolayers (ML) causes a blueshift of PL peak energies as the charge carriers concentrated in the PbS core region. Enhancement of the PL intensity of colloidal PbS and PbS/MnS core shell QDs has been observed when the samples are illuminated above the band gap energy, under continuous irradiation for 40 min. Luminescence from PbS QDs and PbS/MnS core shell QDs can be strongly influenced by the interaction of water molecules and oxygen present in aqueous solution adsorbed on the QD surface. However, PbS/MnS core shell QDs with a shell thickness of 1.5 ML did not show a PL peak energy stability as it was redshifted after 25 min, probably due to wider size distribution of the QDs.

Synergistic Effect of Plasmonic Gold Nanoparticles Decorated Carbon Nanotubes in Quantum Dots/TiO2 for Optoelectronic Devices.

Here, a facile approach to enhance the performance of solar‐driven photoelectrochemical (PEC) water splitting is described by means of the synergistic effects of a hybrid network of plasmonic Au nanoparticles (NPs) decorated on multiwalled carbon nanotubes (CNTs). The device based on TiO2–Au:CNTs hybrid network sensitized with colloidal CdSe/(CdSexS1− x)5/(CdS)1 core/alloyed shell quantum dots (QDs) yields a saturated photocurrent density of 16.10 ± 0.10 mA cm−2 [at 1.0 V vs reversible hydrogen electrode (RHE)] under 1 sun illumination (AM 1.5G, 100 mW cm−2), which is ≈26% higher than the control device. The in‐depth mechanism behind this significant improvement is revealed through a combined experimental and theoretical analysis for QDs/TiO2–Au:CNTs hybrid network and demonstrates the multifaceted impact of plasmonic Au NPs and CNTs: i) hot‐electron injection from Au NPs into CNTs and TiO2; ii) near‐field enhancement of the QDs absorption and carrier generation/separation processes by the plasmonic Au NPs; iii) enhanced photoinjected electron transport due to the highly directional pathways offered by CNTs. These results provide fundamental insights on the properties of QDs/TiO2–Au:CNTs hybrid network, and highlights the possibility to improve the performance of other solar technologies.

Design of Core-Shell Quantum Dots-3D WS2 Nanowall Hybrid Nanostructures with High-Performance Bifunctional Sensing Applications.

Transition metal dichalcogenides (TMDCs) have recently attracted a tremendous amount of attention owing to their superior optical and electrical properties as well as the interesting and various nanostructures that are created by different synthesis processes. However, the atomic thickness of TMDCs limits the light absorption and results in the weak performance of optoelectronic devices, such as photodetectors. Here, we demonstrate the approach to increase the surface area of TMDCs by a one-step synthesis process of TMDC nanowalls from WOx into three-dimensional (3D) WS2 nanowalls. By utilizing a rapid heating and rapid cooling process, the formation of 3D nanowalls with a height of approximately 150 nm standing perpendicularly on top of the substrate can be achieved. The combination of core-shell colloidal quantum dots (QDs) with three different emission wavelengths and 3D WS2 nanowalls further improves the performance of WS2-based photodetector devices, including a photocurrent enhancement of 320-470% and shorter response time. The significant results of the core-shell QD-WS2 hybrid devices can be contributed by the high nonradiative energy transfer efficiency between core-shell QDs and the nanostructured material, which is caused by the spectral overlap between the emission of core-shell QDs and the absorption of WS2. Besides, outstanding NO2 gas-sensing performance of core-shell QDs/WS2 devices can be achieved with an extremely low detection limit of 50 ppb and a fast response time of 26.8 s because of local p-n junctions generated by p-type 3D WS2 nanowalls and n-type core-shell CdSe-ZnS QDs. Our work successfully reveals the energy transfer phenomenon in core-shell QD-WS2 hybrid devices and shows great potential in commercial multifunctional sensing applications.

Impurity states in InGaAsP/InP core–shell quantum dot under external electric field

In the framework of effective mass envelope function approximation, the impurity states are calculated in InGaAsP/InP core–shell quantum dots by plane wave expansion method, and the effect of electric field is considered. The impurity binding energies in 1s and 2p ± states, and the impurity transition energy between 1s state and 2p ± state are calculated and analyzed in detail with the change of shell thickness, core radius, impurity position, and electric field strength. The results show that the impurity states in the core are stable when the shell thickness is more than 0.4a * . The binding energies and transition energies decrease with the increase of core radius. The applied electric field destroys the symmetrical distribution of binding energy and transition energy about the core center. The increase or decrease of the binding energy and transition energy depend upon the position of impurity and the direction of electric field.

86‐5: Late‐News‐Paper: Giant Shell Quantum Dots for Color Conversion and as Active Material in QLEDs

We present an automated and up‐scaled synthesis of giant‐shell QDs (GSQD). For color conversion, these particles will be incorporated in a suitable matrix with high QD content and transferred onto a blue light LED. We will also show results of QLEDs with a thin film of GSQD as active material.

Structure-optical property correlation in CdTe/CdS core-shell quantum dots and their effects on Cu2+ sensing mechanisms

A rapid and simple aqueous method has been developed for synthesizing CdTe/CdS core shell quantum dots (QDs) by refluxing glutathione (GSH) with Cd2+ and Te2− precursors at 100 °C without using inert medium. Here GSH has dual role, i.e., as an in-situ source of sulphide for deposition of CdS on CdTe and as a capping agent to stabilize the CdTe/CdS QDs. As the refluxing time was enhanced from 15 min to 105 min, the sizes of the spherical shaped CdTe/CdS QDs increased from 2.8 ± 0.8 nm to 3.9 ± 1.1 nm, the crystalline nature improved, GSH capping content decreased and the CdS shell deposition was increased. The size dependent change in photoluminescence (PL) from green to red was observed. The photoluminescence quantum yield (PLQY) was improved with refluxing time and maximum PLQY was obtained for the batch synthesized by 60 min refluxing. The PL of these QDs were drastically quenched by ppb levels of Cu2+ ions. Instead of the batch with maximum PLQY, the best Cu2+ sensitivity and selectivity was obtained for the batch synthesized by refluxing for 30 min. This is due to optimal GSH capping content required for availability of Cu2+ ions at the surface of the QDs for favorable electron transfer process, confirmed by PL decay kinetic studies.

Optimizing Quantum Dot Probe Size for Single-Receptor Imaging.

Quantum dots (QDs) are nanocrystals with bright fluorescence and long-term photostability, attributes particularly beneficial for single-molecule imaging and molecular counting in the life sciences. The size of a QD nanocrystal determines its physicochemical and photophysical properties, both of which dictate the success of imaging applications. Larger nanocrystals typically have better optical properties, with higher brightness, red-shifted emission, reduced blinking, and greater stability. However, larger nanocrystals introduce molecular-labeling biases due to steric hindrance and nonspecific binding. Here, we systematically analyze the impact of nanocrystal size on receptor labeling in live and fixed cells. We designed three (core)shell QDs with red emission (600-700 nm) and crystalline sizes of 3.2, 5.5, and 8.3 nm. After coating with the same multidentate polymer, hydrodynamic sizes were 9.2 nm (QD9.2), 13.3 nm (QD13.3), and 17.4 nm (QD17.4), respectively. The QDs were conjugated to streptavidin and applied as probes for biotinylated neurotransmitter receptors. QD9.2 exhibited the highest labeling specificity for receptors in the narrow synaptic cleft (∼20-30 nm) in living neurons. However, for dense receptor labeling for molecular counting in live and fixed HeLa cells, QD13.3 yielded the highest counts. Nonspecific binding rose sharply for hydrodynamic sizes larger than 13.3 nm, with QD17.4 exhibiting particularly diminished specificity. Our comparisons further highlight needs to continue engineering the smallest QDs to increase single-molecule intensity, suppress blinking frequency, and inhibit nonspecific labeling in fixed and permeabilized cells. These results lay a foundation for designing QD probes with further reduced sizes to achieve unbiased labeling for quantitative and single-molecule imaging.

Effects of built-in electric field and donor impurity on linear and nonlinear optical properties of wurtzite InxGa1 – xN/GaN nanostructures**Project supported by the National Natural Science Foundation of China (Grant No. 11947414) and the Research Program of Science and Technology at University of Inner Mongolia Autonomous Region, China (Grant No. NJZZ19001).

The linear and nonlinear optical absorption coefficients (ACs) and refraction index changes (RICs) of 1s–1p, 1p–1d, and 1f–1d transitions are investigated in a wurtzite InxGa1 – xN/GaN core–shell quantum dot (CSQD) with donor impurity by using density matrix approach. The effects of built-in electric field (BEF), ternary mixed crystal (TMC), impurity, and CSQD size are studied in detail. The finite element method is used to calculate the ground and excited energy state energy and wave function. The results reveal that the BEF has a great influence on the linear, nonlinear, and total ACs and RICs. The presence of impurity leads the resonant peaks of the ACs and RICs to be blue-shifted for all transitions, especially for 1s–1p transition. It is also found that the resonant peaks of the ACs and RICs present a red shift with In-composition decreasing or core radius increasing. Moreover, the amplitudes of the ACs and RICs are strongly affected by the incident optical intensity. The absorption saturation is more sensitive without the impurity than with the impurity, and the appearance of absorption saturation requires a larger incident optical intensity when considering the BEF.

Functionalized silver nanoparticles with graphene quantum dots shell layer for effective antibacterial action

Graphene quantum dots (GQDs) as a shell layer was coated on the surface of silver nanoparticles (AgNPs) to obtain an effective antibacterial composite (GQDs@AgNPs). The structures and antibacterial properties of AgNPs, GQDs, and GQDs@AgNPs were studied. SEM and TEM results indicated that GQDs were coated on the surface of AgNPs. For GQDs@AgNPs, the core size of AgNPs was about 20 nm, and the shell thickness of GQDs was about 5 nm. The formation and antibacterial mechanism of GQDs@AgNPs composite materials were discussed in detail. It showed excellent antibacterial properties for E. coli and S. aureus.

Effect of Polymer Capping on Photonic Multi-Core–Shell Quantum Dots CdSe/CdS/ZnS: Impact of Sunlight and Antibacterial Activity

The highly luminescent CdSe/CdS/ZnS core–multi-shell quantum dots (QDs) were prepared without a protective atmosphere through the precursor injection method (phosphine free) in paraffin liquid and oleic acid. Polymers (PEG, PVA, PVP, and PAA) were coated to CdSe/CdS/ZnS core–multi-shell quantum dots to increase stability. However, core–multi-shell structured QDs reveal enhanced emission in the range 355–410 nm by suppressing the defect sensitive cores and nonradioactive recombination in PL spectra. The cubic zinc blended quantum dots with crystallite size in the range 22–44 nm, as confirmed by XRD, were obtained. The resultant absorption spectra of all the samples showed that the samples were absorbent in the UV region over the 302–380 nm range. In the FT-IR spectrum 712, 731, and 400–700 cm–1 band values were assigned to CdSe, CdS, and ZnS band stretching, respectively. Images of CdSe, CdSe/CdS, and CdSe/CdS/ZnS quantum dots obtained from the SEM were spherical whereas QDs capped with different polymers (PEG, PVA, PVP, and PAA) showed nanofibers that were linear and homogeneous size ranged between 12 and 38 nm. These as prepared QDs were placed under visible light for 48 h. After absorbing UV light, the range of UV–vis intensity was enhanced until 389–464 nm and emission intensity enhanced until 492–509 nm, which was confirmed by UV and PL spectra. CdSe/CdS/ZnS QDs with organic ligands revealed antibacterial activity over a broad range against Klebsiella Pneumoniae and Pseudomonas aeruginosa.

Functional Memristors: Optically Modulated Threshold Switching in Core–Shell Quantum Dot Based Memristive Device (Adv. Funct. Mater. 16/2020)

Functional Memristors: Optically Modulated Threshold Switching in Core–Shell Quantum Dot Based Memristive Device (Adv. Funct. Mater. 16/2020)

Energy Transfer between Perovskites and CdSe/ZnS Core–shell Quantum Dots

Energy Transfer between Perovskites and CdSe/ZnS Core–shell Quantum Dots

Controlled Synthesis of Ag2 Te@Ag2 S Core-Shell Quantum Dots with Enhanced and Tunable Fluorescence in the Second Near-Infrared Window.

Fluorescence in the second near-infrared window (NIR-II, 900-1700 nm) has drawn great interest for bioimaging, owing to its high tissue penetration depth and high spatiotemporal resolution. NIR-II fluorophores with high photoluminescence quantum yield (PLQY) and stability along with high biocompatibility are urgently pursued. In this work, a Ag-rich Ag2 Te quantum dots (QDs) surface with sulfur source is successfully engineered to prepare a larger bandgap of Ag2 S shell to passivate the Ag2 Te core via a facile colloidal route, which greatly enhances the PLQY of Ag2 Te QDs and significantly improves the stability of Ag2 Te QDs. This strategy works well with different sized core Ag2 Te QDs so that the NIR-II PL can be tuned in a wide range. In vivo imaging using the as-prepared Ag2 Te@Ag2 S QDs presents much higher spatial resolution images of organs and vascular structures as compared with the same dose of Ag2 Te nanoprobes administrated, suggesting the success of the core-shell synthetic strategy and the potential biomedical applications of core-shell NIR-II nanoprobes.

Features of Plasmon Switching in a Graphene Nanoresonator Loaded with a Shell Quantum Dot

Plasmon switching is considered for surface plasmon–polaritons in a graphene waveguide integrated with a stub nanoresonator containing a quantum dot. The described effect is observed for infrared electromagnetic waves localized in a device with dimensions of 20 nm.